Fixed possible duplicated join of article table.
Fixed possible duplicated join of article table.

mburggraf/otrs,rudy500/otrs,s7design/otrs,s7design/otrs,s7design/otrs,mburggraf/otrs,rudy500/otrs,rudy500/otrs,xhoy/otrs,xhoy/otrs,rudy500/otrs,mburggraf/otrs,mburggraf/otrs,s7design/otrs,rudy500/otrs,xhoy/otrs,mburggraf/otrs,xhoy/otrs,xhoy/otrs,s7design/otrs